Plutonium and uranium has been stored in plastic bottles, he warns.

A fire at Britain’s most hazardous nuclear site would create a “plume of radiological waste that will go across Western Europe”, a whistleblower has warned.

Parts of the plant in Cumbria, the most hazardous in Britain, have too few staff to operate safely and radioactive plutonium and uranium has been stored in degrading plastic bottles for years that were only intended to be temporary, a BBC Panorama investigation claims.

Between July 2012 and July 2013 there were 97 incidents where parts of the site had too few people working.

The whistleblower, a former senior manager, said a fire in a nuclear waste silo or processing plant was his biggest fear, telling the programme: “If there is a fire there it could generate a plume of radiological waste that will go across Western Europe.”

Sellafield, which reprocesses and stores nearly all of Britain’s nuclear waste, said safety has been improved in recent years but minimum safe manning levels are still being breached on average once a week, Panorama found.

MP Meg Hillier, who chairs parliament’s Public Accounts Committee, said: “It is incredible. It defies belief actually that, that anything could be working at below safe staffing levels. There is no excuse.”

Dr Rex Strong, head of nuclear safety at Sellafield, denied that operating below these levels was dangerous.

“You make alternative arrangements, so the things that have to be done get done. Facilities are shut down if we’re not able to operate them in the way that we want to,” he told Panorama.

“Safety is our priority and we are managing a very complex site which has got a great deal of hazardous radioactive materials on it.”

BBC Panorama
Dr Rex Strong, head of nuclear safety at Sellafield, said: 'Safety is our priority and we are managing a very complex site'.

He added that the plant was working to get the material into proper storage: “The organisation is now focusing on putting right some under investments of the past in order to support the hazard and waste reduction mission that the site has.”

Sellafield said it was “simply not true” to suggest plutonium and uranium was “inappropriately managed” at the site.

But Panorama claims to have been leaked reports that suggest “Sellafield had problems with emergency management and with maintaining the site’s infrastructure”.

One from 2013 says “years of neglect” had led to “intolerable conditions”, Panorama said.

Panorama’s Sellafield’s Nuclear Safety Failings is on BBC One at 8.30pm on September 5.